Elimination of arcing effects in circuit breakers



Sept. 16, 1969 A. R. NORDEN E 3,467,799

ELIMINATION OF ARCING EFFECTS IN CIRCUIT BREAKERS Filed Dec.

5 m z w 1 lllrl i Z fl l lU lH my rifllfl x -||L. w r a a w "fa x 6 M 27 w w// z a w m Q INVENTORS A4 "AA Me A. ,vupnv United States Patent3,467,799 ELIMINATION OF ARCING EFFECTS IN CIRCUIT BREAKERS Alexander R.Norden, New York, and George W. Knecht, Brooklyn, N.Y., assignors toMurray Manufacturing Corporation, Brooklyn, N.Y., a corporation of NewYork Filed Dec. 8, 1965, Ser. No. 512,438 Int. Cl. H01h 9/44, 33/18 US.Cl. 200-147 6 Claims ABSTRACT OF THE DISCLOSURE In order to eliminatethe deteriorating effects of arcover in electromagnetic circuitbreakers, a runner of magnetic material, electrically coupled to one ofthe contacts and magnetically coupled to the magnetic circuit isdisposed proximate one contact to take over the arc,upon contactseparation.

This invention relates to circuit breakers in general and in particularto an improvement in circuit breakers of'the electromagnetic type foreliminating the effects of arcing.

It is often desirable, if not necessary, to protect electrical circuitsagainst shorts and overload conditions as well as to provide means forcontrolling the operational status of the associated equipment via amanually operable switch. Because a circuit breaker is capable ofserving both these functions, it has enjoyed widespread commercial andhousehold application.

The protection provided by a circuit breaker is automatic; the breakerresponding to a predetermined current condition to open the contactsmaintaining the lineto-load continuity. As a rule, the breaker is set bymanually closing the electrical contacts through a trippa-ble linkage,the linkage being actuated by a current-responsive device to trip uponoverload, either immediately or after a predetermined overload time,thereby opening the contacts. In magnetic breakers the tripping force isprovided by the magnetic flux induced by a coil through which the loadcurrent passes; the fiux acting upon a magnetic element which directlyor indirectly unlatches the linkage. Reset, which is to be distinguishedfrom the reclosing of the contacts, is either automatic or manual, andin the latter case, is effected by urging the breaker handle to the fullOFF position. Subsequently, by placing the handle in the ON position,the circuit continuity is reestablished by the resultant closing of thecontacts.

Because breakers must respond to and interrupt a short circuit conditionby automatically breaking the lineto-load continuity, arc-over is aserious problem. This problem also exists in breakers of large capacitywhere a line-to-load continuity is manually broken during heavyinductive load conditions. No solution to this problem has provedcompletely satisfactory, and recent advances in breaker technology whichallows breaker miniaturization tend to accentuate the problem ratherthan relieve it.

In an attempt -to obviate the tendency of the arc to transfer to theneck of the moving contact (burning away a portion, and eventually allof the contact arm), a variety of arm configurations have been proposed.All, however, met with only moderate success. A more satisfactorysolution is predicated on the use of an arc runner. This is a piece ofmagnetic material electrically connected to the stationary contact andso arranged that the arc transfers to it as soon as contact continuityis broken. The are then travels along the runner, length- 3,467,799Patented Sept. 16, 1969 ening and finally extinguishing. Thisarrangement substantially ameliorates the deteriorating effect of theare on breaker components. However, it gives rise to a Verydisadvantageous side effect. When the arc is transferred, it melts someof the runner metal and expels it in the form of red hot globulesthrough the adjacent gas vent, thus creating a serious fire risk. Whilethis problem may be alleviated by including a de-ion arcchute totrap theglobules, the trap location and size raise considerations diametricallyopposed to miniaturizing the breaker.

Accordingly it is the object of this invention to provide an arrangementwithin the circuit breaker which obviates the deleterious effect ofarc-over and does so in a simple inexpensive manner withoutnecessitating additional room within the breaker.

The above mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will best be understood by reference to the following descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawings wherein the single figure illustrates the circuitbreaker according to the invention with casing portions cut away toreveal those internal portions necessary for an understanding of theinvention.

The circuit breaker shown in the figure is, except for the inventivemodification, identical to that depicted and described in copendingapplication Ser. No. 388,259, filed Aug. 7, 1964 to the same assignee.While the description which follows is intended to be complete insofaras necessary for an understanding of the invention, reference may be hadto above alluded to application for an illustration of a completecircuit breaker in which the invention may be used.

The circuit breaker casing 10 is preferably molded of insular material,such as Bakelite, and consists of two complementary interlockingsections (each having its main plane parallel the plane of the paper)held together by rivets 12. The lower forward portion of the casing isomitted on both sides of the'breaker at 10' to expose contact 13 adaptedto engage in sidewiping fashion a panelboard bus bar stab, carrying linevoltage.

Aflixed to the contact 13, for example by welding to its upper portion(concealed) is one end of the electromagnetic coil 14, the other end ofwhich is led to the stationary contact member 15 carrying contact 15'. Acomplementary movable contact 16 is borne by the contact arm 16 pivotedbetween its extremities at 17. A flexible line 19 electrically connectsthis arm to the circuit breaker load terminal.

When the circuit breaker handle 20 is rotated clockwise a trippablelinkage (not shown) bears upon the left end of contact arm 16, rotatingit clockwise and closing the contacts.

Coil 14 is in series with the load and therefore carries the loadcurrent; generating a magnetornotive force (MMF) directly dependent uponthe value of this current.

Preferably the electromagnet is of the type described in US. Patent No.2,890,306 issued June 9, 1959 to the same assignee. That is, theelectromagnet includes a core piece 40, freely disposed in a fluidmedium within tubular member 21. As described in the patent when thecurrent and therefore the MMF reaches a predetermined magnitude the coremoves up decreasing the reluctance of the magnetic loop including thecore, the side armature 23, bottom armature 26, and movable armature 24.The force upon the movable armature at the air gap 22 is dependent uponthe flux density which in turn is inversely dependent upon thereluctance and consequently,

after a predetermined time (during which the core is moving up), theforce of attraction surmounts the spring bias force 27 and the movablearmature 24 rotates clockwise to eliminate the air gap. The resultanteffect of the foregoing is the lifting of the retaining latch 24 whichin turn triggers the contact opening linkage (a portion 30' of which isshown), thereby driving contacts 15 and 16' apart.

According to the invention, a second magnetic field or flux loop isprovided which includes the bottom armature 26, the core 40, an air gap30, and an extension 23' on the side armature, so formed and positionedthat it acts as an arc runner. That is, this extension which iselectrically connected for example at 26' to the stationary contactmember 15 is sufliciently proximate contact 15' that it takes over theare leading it away from both contact members and towards vent 32.

Ordinarily, one would expect the arc to cause hot globules to emanatefrom the arc runner and spew out the vent. However, quite the oppositeoccurs, and instead of being expelled, the globules are attracted andheld at the end of the arc runner, the runner showing little erosionafter repeated tests. This phenomenon may be accounted for as follows:

When a short occurs (a condition which would cause severe arcing) anextremely large magnetic field is produced whose flux density issufiicient to trip the linkage without the movement of core 40. Hence asufiicient por- 4 nate the lower armature 26, utilizing the arc runneralone to complete the flux path through themain air gap 22.

This arrangement will slightly reduce the efficiency of the mainfunction of the electromagnet i.e. tripping the linkage, however, itwillmake more flux available to the arc runner.

We claim:

1. In a circuit breaker of the type having at least one pair ofcontacts, the separation of which is dependent upon a load-currentdependent coil energizing a magnetic circuit through an armature memberpositioned adjacent said coil, the improvement for eliminating thedeteriorat- 1ng etfects of arc-overcomprising, a runner of magneticmaterial electrically coupled to one of said pair of contacts,magnetically and physically connected to the armature of said magneticcircuit, and disposed proximate said one contact to take over the arctherefrom on contact separation.

coil.

tion of this core is available in the described second flux loop tosustain a second magnetic field of high flux density. Thus the ironglobules which form are attracted and held to the runner.

Similarly, when the breaker is under a large load and is manuallytripped, the second loop whose flux magnitude is commensurate in sizewith the load current, will function to effectuate the same result. Thearrangement according to the invention is self-controlling; that is, thegreater the current, the greater the arc, and hence the greater themagnetic field necessary to hold the globules. Since the arc representscoil, as well as load current, the greater the arc, the greater the coilcurrent available to hold the globules and hence the desired objectiveis automatically obtained.

Needless to say, while the depicted magnetic circuit includes dual fluxpaths the existence of the two paths depends a great deal upon the coreconfiguration. With some cores (e.g. stationary ones) it may beexpedient to elimi- 2. The improvement claimed in claim 1 which said arerunner is positioned adjacent one end of said coil.

3. The improvement claimed in claim 2 in which said armature is a sidearmature substantially parallel said 4. The improvement claimed in claim3 in which said runner is angled with respect to said side armature andextends toward said coil end.

5. The improvement claimed in claim 1 in which the magnetic circuitincludes a core slid able into said coil upon the energization thereof,a first flux loop including said coil and a portion of said core, and asecond flux loop including a portion of said core and the arc runner.

6. The improvement claimed in claim 5 in which said first and secondflux loops include an E shaped armature the middle branch of the B beingcommon to the two loops and the lower branch being the arc runner.

References Cited UNITED STATES PATENTS 2,575,730 11/1951 Sandin et al.

1,391,966 9/1921 Moller 335201 XR 2,192,059 2/1940 Willmann 335-201XR3,189,716 6/1965 Hugus 200-147 ROBERT S. MACON, Primary Examiner U.S.Cl. X.R. 335-201

